Optical analysis of complex multilayer structures using multiple data types

Variable angle of incidence spectroscopic ellipsometiy (VASE) is commonly used for multilayer optical analysis, but in some cases this experiment (performed in reflection) does not provide sufficient information for the unique determination of the thicknesses and optical constants of the films in the given multilayer. We have found that augmenting the VASE data with data from other optical experiments greatly increases the amount of information which can be obtained for multilayers, particularly when they are deposited on transparent substrates. In this work, we describe a formalism which allows us to quantitatively characterize complex multilayer structures by using combined reflection and transmission ellipsometry, reflection ellipsometiy with the sample flipped over, and intensity transmission measurements. To demonstrate the usefulness of this capability, the analysis of a complex graded, absorbing thin film structure (a Cr-based phase-shifting photomask blank), is presented.